Three-dimensional memory devices provide high density memory for modern electronic devices. Examples of three-dimensional memory devices include three-dimensional NAND memory devices and Resistance Random Access Memory (ReRAM) devices.
Three-dimensional vertical NAND strings having one bit per cell for a three-dimensional NAND memory device are disclosed in an article by T. Endoh et al., titled “Novel Ultra High Density Memory With A Stacked-Surrounding Gate Transistor (S-SGT) Structured Cell”, IEDM Proc. (2001) 33-36. In a three-dimensional vertical NAND memory device, data is stored as presence or absence of trapped electrical charges in a vertical string of memory elements, which may be portions of a continuous charge trapping material layer or discrete floating gate electrodes. Electrically conductive layers can be provided at each level of the memory elements, and can function as word lines. A semiconductor channel and a tunneling dielectric can be provided adjacent to the vertical string of memory elements to program, and to read, the stored electrical charges in the vertical string of memory elements.
A ReRAM is a non-volatile memory device employing reversible change in resistance in a thin film with application of electrical voltage bias across the film. Application of the electrical voltage bias in one manner can cause decrease in the resistance of the thin film, for example, by formation of filaments that function as leakage current paths or by increasing a crystallinity of the thin film. Application of a different type of electrical voltage bias can cause reversal of the resistance of the thin film to an original high-resistance state, such as by removal of the filaments from the thin film or by decreasing the crystallinity of the thin film. Thus, data can be stored in a ReRAM cell by changing the resistance of the thin film, which can be a solid-state material. The thin film is referred to as a memory film or a read/write film. Examples of ReRAM devices are described in World Intellectual Property Organization (WIPO) Publication No. WO2007004843 A1 to Hong et al. and U.S. Patent Application Publication No. 2013/0043455 A1 to Bateman.
A barrier modulated cell (BMC) resistive random access memory (ReRAM) device is a ReRAM in which the resistance of a memory element is modulated by separation or recombination of oxygen vacancies and interstitial oxygen ions. When the interstitial oxygen ions combine with the oxygen vacancies, a zone with a low density of charge carriers is formed due to elimination of oxygen vacancies, thereby increasing the resistance of the memory element. This operation is herein referred to as a “resetting” operation. When the oxygen ions are separated from the oxygen vacancies, a zone with a high density of charge carriers is formed due to the presence of vacancies, thereby decreasing the resistance of the memory element. This operation is herein referred to as a “setting” operation.